The present invention relates to an autonomous power supply for an observation device using at least one electrooptical modulator cell having a capacitive effect and containing an electrooptical material, working with a system of control electrodes receiving high-amplitude electrical signals, and including clock systems to time the periodic application of electrical control signals to the electrooptical cell electrodes.
Stereoscopic image observation devices are known that use a pair of glasses including one right-hand and one left-hand device, through which a person can observe an image with the right eye and with the left eye, respectively. The right-hand and left-hand devices each include a capacitive-effect electrooptical cell consisting of an electrooptical material, e.g. of the PLZT type, and the associated control electrodes. Control signals are applied alternately to the control electrodes of the two electrooptical cells, to allow the light itself to be transmitted alternatively through the right-hand and left-hand devices, each of which includes one such cell, and thus create a stereoscopic effect. When observing television or movie images, the alternating control voltages applied to the right and left devices of the eyeglasses must also be synchronized with the image sequencing laws. This can be done, for example, by having the television receiver emit a carrier wave of the infrared or ultrasonic type, for example, modulated by a synchronization signal, or by having the image itself carry specific "right" and "left" information. The stereoscopic image observation apparatus must then be equipped with the means for receiving this modulated carrier wave, so that the synchronization information can be extracted, to apply the control signals alternately to the right and left parts of the spectacles.
The control voltages applied to the capacitive effect electrooptical cells are particularly high, and can be of the order of 1000 V. Consequently, the use of such high voltages may be dangerous to the person using the stereoscopic image observation device, particularly if the high voltage generator is mounted directly on the pair of glasses.
In classical stereoscopic image observation systems, the high voltage needed is first created in a high-voltage generator circuit that can produce a continuous high voltage, and this high voltage is then switched alternately to each pair of electrodes associated with one cell. This means that the converter or high voltage generator is operating continuously, and the current applied to the electrooptical cell electrodes cannot be limited easily and simply except by inserting a resistance, which wastes power and affects the speed of the transient signals. Furthermore, a capacitive storage element must be available that is much larger than the electrooptical cells, and this storage element constitutes a energy tank that may be dangerous. Moreover, switches that operate on high-level continuous direct current are relatively complicated.
The purpose of the present invention is precisely to remedy the above-identified disadvantages with an autonomous power supply that offers a high level of safety, compactness, low power consumption and good stability of the signals generated, while it is still possible to adjust the voltage to take the dispersions into account, and obtain a high switching speed on highly capacitive loads.
These purposes are achieved by a supply device of the type defined at the beginning of the description which, according to the invention, includes a low-voltage power source, a circuit creating intermittent high voltage from the low voltage power source, a set of switches placed between the circuit creating the intermittent high voltage and the electrode system of the said electrooptical cells, and circuits processing the clock signals to control the said circuit creating intermittent high voltages, as well as the said switches.
The invention, with a pulsed-type high voltage generator, stores the low-voltage power and operates at high voltage only at the time the power is transferred to the electrooptical cells. It is thus possible to control the current levels involved, and especially to supply power to the electrooptical cells just at the transitions prior to the front switching transinent of the cell state, since the capacitance of the electrooptical cells allows them to maintain a charge even when they are disconnected from the high-voltage source. The invention also easily recovers energy during the switchover from one cell to the other.
The present invention can be used just as well for single-window type observation devices having a single capacitive-effect electrooptical cell, as with binocular type observation devices having a first and second capacitive-effect electrooptical cell, each coordinated by a system of electrodes. In the latter case, the clock signal processing circuits may include synchronization systems that can receive a synchronization signal from the outside world to control sequentially the said circuit creating intermittent high voltage, and the said switches.
In one embodiment of the present invention, the autonomous power supply, used with stereoscopic glasses, includes a system for receiving a carrier wave modulated by synchronization signals that periodically trigger high-amplitude electric control signals applied alternately to the electrode systems of the first and second cells, and the clock signal processing circuits include circuits for processing the synchronization signals received by the said carrier reception system, to sequence the said circuit creating the intermittent high voltage, and the said switches.
One major characteristic of the present invention is that the circuit creating the intermittent high voltage includes a coil and a switching component, mounted in series at the terminals of the low-voltage power source, as well as a capacitor connected in parallel with the switching component, and the said switching component is controlled periodically by the signal processing circuits.
Preferably, the device as invented includes a first switch connected between the common point of the coil and switching component and one electrode of one of the capacitive-effect electrooptical cells. The first switch is controlled in such a way that it is closed as soon as the switching component begins to open, for a time smaller than the aperture duration of said switching component.
The autonomous power supply may also include a second switch, mounted between the said electrode of one of the electrooptical cells and the end of the inductance coil connected through an anti-feedback diode to the low-voltage power source, and the said second switch is controlled in such a way that it is closed from the time the switching component begins to close, for a time smaller than the closed state duration of said switching component.
In another embodiment, the autonomous power supply includes a first and third switch circuited between the common point of the inductance coil and the switching component and one electrode of the first and second electrooptical cells, respectively. Second and fourth switches are circuited between the side of the inductance coil connected through an anti-feedback diode to the low-voltage power source, and the common point between the first switch and the first electrooptical cell and the common point between the third switch and the second electrooptical cell. The first and fourth switches are controlled in such a way as to be closed simultaneously as soon as the switching component begins to open, at every two periods of the switching component control signal. The second and third switches are controlled in such a way as to be closed simultaneously as soon as the switching component begins to open. During the switching component control signal periods, the first and fourth switches remain open continuously, and the time during which the first, second, third and fourth switches is closed is always less than the time the switching component stays open.
According to other particular characteristics, a clipping diode is placed in parallel with the capacitor, which is placed in parallel with the switching component, and a diode may also be connected in series with the said switching component, at the terminals of the said capacitor, for protection.
As per the invention, it is advantageous to include in the device a circuit that modulates the duration of the switching component closing control signal.
For this purpose, the device can include a divider bridge measuring the high voltage applied periodically to the point in common between the inductance coil and the switching component, a sample-and-hold circuit, a comparator to detect the difference between the sampled voltage and a reference voltage V.sub.ref, and a circuit that, as a function of the signal output by the said comparator, applies a delay to the signal controlling the closing of the switching component.
The circuits processing the synchronization signals received by the receiving system may include a phase-locked loop and a programmable matrix of logic circuits for controlling the switching sequences of the switches.
In a particular configuration, the switch controls are of the floating type and include a high-voltage switching component such as a bipolar transistor, a field effect transistor or a thyristor, placed in the diagonal of a diode bridge, and an isolator to apply a control signal to the switching component.
The isolator is preferably of the piezoelectric isolator or rectilinear transformer operating at resonance.
The low-voltage power source, the circuit creating intermittent high voltage, all of the switches and the circuits processing the synchronization signals are carried in a portable unit that is connected to the reception systems and to the first and second cells by three or four electrical connection wires.
In a first possible mode of operation, all of the switches have floating control, and provide bipolar control of the high voltage applied to the electrodes of the first and second electrooptical cells.
In another possible mode of operation, all of the switches provide single-pole control of the high voltage applied to the electrodes of the first and second electrooptical cells.
In the latter case, the switches can each include a field effect transistor, an auxiliary capacitor placed between the grid and the source of the said field effect transistor, a diode connected in series with the drain-source space of the said field effect transistor, and an isolator.